Here's a study about the effects of video games that matches my preconceptions: Kids who are "less agreeable, less conscientious and easily angered" can become more hostile by playing them. Other kids learn useful social skills. People vary, and the way they respond to a type of stimulus varies.
They used the Five-Factor Model (neuroticism, extraversion, openness to experience, agreeableness and conscientiousness) and found that kids high in neuroticism and low in agreeableness and conscientiousness reacted worst to violent video games. Kids without this confluence of traits were not affected.
Since I believe that model has a biological substrate, it follows that video games affect kids differently according to the biology their brains.